My laboratory has demonstrated that the transition of quiescent Balb/c-3T3 cells from growth arrest into S phase can be separated into two stages under the control of separate serum growth hormones. The first stage -"competence" - is regulated by the PDGF component of serum and occurs independently of RNA or protein synthesis. The second stage -"progression" -is regulated by somatomedins and other cofactors contained in platelet-poor plasma; progression requires both RNA and protein synthesis. In contrast to serum growth factors which provide either competence or progression activities (but never both), SV40 infection provides both competence and progression activities. The proposed research has three objectives. First, we wish to define the separate roles of somatomedins and plasma cofactors in controlling the progression of Balb/c-3T3 cells through G1 and S phase. Second, we wish to establish functional analogies between the transformation proteins of animal tumor viruses and the serum growth factors which regulate competence and progression. As a third objective, we wish to study regulation of RNA and protein metabolism by growth factors and virus transformation proteins using in vitro systems. We will develop a defined culture medium which will support the progression of Balb/c-3T3 cells from G0 into S phase; this defined medium will be used to analyze the cellular response to pure somatomedins. Temperature sensitive or deletion mutants of animal tumor viruses will be used to study the functions of tumor virus transformation proteins; by examining the ability of individual growth factors to complement virus genetic defects in defined culture medium we will be able to assign growth regulatory functions to individual virus gene products. In vitro assays for eukaryotic initiation factors and cell free translation systems will be used to probe the regulation of mRNA and protein metabolism as Balb/c-3T3 cells progress through G1.